#include<bits/stdc++.h>
using namespace std;
const int N = 510;
int n, m;
int g[N][N];//邻接矩阵
int dist[N];
bool st[N];
int dijkstra(){
    memset(dist, 0x3f, sizeof dist);
    dist[1] = 0;
    for(int i = 1; i <= n; i ++){
        int t = -1;
        for(int j = 1; j <= n; j ++){
            if(!st[j] && (t == -1 || dist[t] > dist[j])) t = j;
        }
        st[t] = true;
        for(int j = 1; j <= n; j ++){
            dist[j] = min(dist[j], dist[t] + g[t][j]);
        }
    }
    if(dist[n] == 0x3f3f3f3f) return -1;
    return dist[n];
}
int main(){
    cin >> n >> m;
    memset(g, 0x3f, sizeof g);
    while(m --){
        int a, b, c;
        cin >> a >> b >> c;
        g[a][b] = min(g[a][b], c);
    }
    cout << dijkstra() << endl;
    return 0;
}